Failure check circuit

ABSTRACT

The failure state, due to disconnection or grounding of resistors connected in parallel, is checked in such a way that diodes are connected in series, respectively between the resistors and a common terminal for the parallel connection. A check signal is supplied to the other common terminal for the parallel connection, and the signals appearing at the connection points between the resistors and the diode are compared with the supplied check signal by using a logic circuit such as an AND gate.

United States Patent 191 Iwasaki et a1.

FAILURE CHECK CIRCUIT Inventors: Takasiro Iwasaki, Tokyo; Sizuhisa Watanabe, Katsuta; Takahiko Tanigami, Mito, all of Japan Assignees: Hitachi, Ltd.; Nissan Jidosha Kabushikikaisha, both of Tokyo, Japan 4 Filed: Mar. 27, 1972 App]. No.: 238,333

Foreign Application Priority Data Mar. 26, 1971 Japan 46-17222 U.S.'Cl 340/214 R, 340/248 E Int. Cl. G08b 23/00 Field of Search 340/214 R, 248 E References Cited UNITED STATES PATENTS 8/1951 Quinn 340/213 UX FREMNCY DIVIDER l PULSE GENERAT FMCY DNIIR 2 FREMNCY UVIDER 3 FREouencY DIVIDER 4 51 Apr. 9, 1974 2,839,741 6/l958 Kratville 340/214 R 3,328,692 6/1967 Lyon 3,537,089 10/1970 Lee 340/214 X Primary Examinerl-larold l. Pitts Attorney, Agent, or Firm-Craig and Antonelli [57] ABSTRACT The failure state, due to disconnection or grounding of resistors connected in parallel, is checked in such a way that diodes are connected in series, respectively between the resistors and a common terminal for the parallel connection. A check signal is supplied to the other common terminal for the parallel connection, and the signals appearing at the connection points between the resistors and the diode are compared with the supplied check signal by using a logic circuit such as an AND gate.

15 Claims, 2 Drawing Figures ETECTOR l PULSE MTECTOR 2 PAIENTEDAPR 91914 PULSE DETECTOR l P3 El PT 05 v PULSE DETECTOR 2 Fig l FREQUENCY mvmen PULSE GENERAT rnemcv DIVDER 2 FREQUENCY DIVIDER :5

FREOLENCY DIVIDER 4 Fig.2

1 FAILURE CHECK CIRCUIT BACKGROUND OF THE INVENTION This invention relates to a failure checking circuit to detect an abnormal or state of failure in which at least one circuit element is open circuited or grounded comprising a plurality of circuit elements which are connected in parallel. This invention particularly relates to a circuit for checking a failure due to disconnection or short-circuiting of elements in a firing circuit system for the protection of occupants of a vehicle in the event of a crash.

Recently, there has been proposed and developed to provide a car with safety means such as an air-bag system or a gas-bag system for restraining the occupants of a vehicle to provide protection for the occupants in the event of a crash. The air-bag system comprises detector means for detecting a crash, high-pressure gas cylinders, air-bags which are quickly enlarged in the crash to restrain the vehicle occupants, and firing means for destroying or removing the valves provided between the high-pressure gas cylinders and the air bags. The firing means comprise circuit elements such as resistors of low resistance, so called firing balls, which are operated by output signals from a detector means in the event of a crash and fire or explode as a result of the heat which the electric current flowing through the resistors generates. Four to eight of these air-bags are provided in a car and, therefore, four to eight firing means are electrically connected in parallel to the detector means.

Since it is absolutely necessary for this kind of safety means to operate with certainty in the event of a crash, it is always necessary to monitor the existence of a failure in the system and warn the driver of the failure.

In order to check for disconnection or grounding of each circuit element, such as the above-mentioned resistors, each circuit line, including the circuit element, must be electrically isolated as to a check signal other than its own signal, since a plurality of circuit elements, such as resistors, are connected in parallel in the airbag system. It is also noted that if the mean value of the electric current flowing through a resistor, as the check signal, is large, the heat generated in the resistor might blow up the explosives, whereby the air-bag system might operate and restrain the driver and possibly cause a traffic accident. Therefore, it is necessary to use an electric current having a small mean value, as the failure check signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a failure check circuit in which the failure of each circuit element can be separately or independently checked in a circuit with a plurality of circuit elements connected in parallel. I

Another object of this invention is to provide a failure check circuit in a circuit comprising a plurality of firing means connected in parallel, for checking the failure state of the firing means without actually operating them.

A further object of this invention is to provide a failure check circuit in a firing circuit comprising a plurality of resistors, having a low resistance, connected in parallel, wherein the mean value of the electric current, flowing through a resistor as a check signal, is small.

Still a further object of this invention is to provide a check system suitable for use in an air-bag protection system for vehicles.

To obtain the above-mentioned objects, the failure check circuit according to the present invention comprises a plurality of serial unit circuits each comprising a circuit element such as resistor and a diode connected in series; connection means for electrically connecting the serial unit circuits in parallel between a first and a second common terminal; signal supply means for supplying an electrical signal to the first common terminal; detecting means for detecting the failure state of the circuit elements having a plurality of input terminals and an output terminal; and connection means for electrically connecting the input terminals respectively with the connection points between the circuit elements and the diodes. I

A failure check circuit according to an embodiment of the present invention comprises a plurality of serial unit circuits each comprising a first diode, a circuit element such as resistor and a second diode which are connected in series; and connection means for electrically connecting the serial unit circuits in parallel between a first and a second common terminal. A check signal such as a pulse signal is supplied to the first common terminal and the output signals appearing at the connection points between the circuit elements and the second diodes are checked through a detector for detecting the failure of the circuit elements, and/or wherein check signals such as pulse signalsare supplied to the connection points between the'first diodes and the circuit elements and an output signal appearing at the second common terminal is checked, through a detector for detecting the failure of the circuit elements.

These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a failure check circuit according to an embodiment of this invention which is applied to an air-bag system; and 2 FIG. 2 shows waveforms of the output pulse signals of the pulse generator and the frequency dividers which are used in the circuit of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, reference numerals 1 and 2 show terminals which are connected to a power source (not shown), reference letters B, to B are circuit elements such as resistors of about 1 to 5 ohms for firing air bags (not shown), reference letters D to D are diodes, reference letters S and S are crash-detect switches comprising mechanical switches which close in the event of a crash of a vehicle and reference letter R is a load resistor of more than 500 k0, and wherein the frequency dividers respectively each comprises, for example, a flip-flop circuit. The resistors for firing air bags (hereinafter referred as to fire-resistors B to B areeach respectively connected to one end of the diodes D, to D through terminals or connection points P to P and the other ends of the diodes D to D, are connected together to the crash-detect switch 8, through the first common connecting terminal P The other ends of the fire-resistors B, to B, are connected respectively to each one end of the diodes D to D through terminals or connection points P to P,,, and the other ends of the diodes D to D,., are connected to the crash-detect switch S through the second common connecting terminal P A check signal is supplied from the pulse signal generator to the first common terminal P,, to the frequency dividers F, to F, and to an input terminal of the pulse detector A,. Output terminals of the frequency dividers F, to F are respectively connected to the connecting terminals or points P to P between the fire-resistors B, to B, and thediodes D, to D The input terminals of the pulse detector A, are connected to the second common terminal P and to each output terminal of the frequency dividers F, to F The input terminals of the pulse detector A are connected to each of the connecting terminals or points P to P between the fire-resistors B, to B, and the diodes D to D,.,. These pulse detectors A, and A comprise logic circuits, for example, AND circuits in which an output signal appears at the output terminal only when input pulse signals are simultaneously supplied to the input terminals thereof. For example, the detector A operates to cause an output pulse signal to appear at the output terminal thereof only when the pulse signal transmitted from the pulse signal generator PG and the pulse signals transmitted through the connection points P to P, between the fire-resistors B, to B and the diodes D to D, are simultaneously applied to the input terminals of the detector A,. Output terminals of the pulse detectors are connected with alarm circuits (not shown) such as a lamp and a buzzer circuit in order to provide a warning to the driver etc. of an abnormal state in the system.

Referring now to FIG. 2, reference letters V V V V and V show waveforms of the output signals from the pulse signal generator PG and frequency dividers F, to F respectively. In the drawing the axis of the abscissa is used to show time t.

The operation of the main circuit as shown in FIG. 1 is briefly explained as follows. Between the terminals 1 and 2, is connected a power source circuit such as a battery and a charged-up condensor, whereby a positive voltage is applied to the terminal 1 in case the diodes D, to D are connected with a polarity as shown in FIG. 1. If a crash occurs, the crash-detect switches 'S, and 5, close or are in the ON condition and a large amount of current flows through the fire-resistors B, to B, in order to operate the air-bag system. Under conditions other than a crash, however, the crash detect switches S, and S, are open or in the OFF" state. 7

In a condition other than a crash, it is always necessary to check whether the fire-resistors B, to B, are defective or have failed. According to the present invention such a check can be effectively carried out as follows:

l. The normal state of the fire-resistors B, to B In case all the fire-resistors B, to B, are in good condition or normally connected, namely, in case none of the fire-resistors B, to B, is disconnected or grounded, pulse signals appear at all the connection points P to P,,, between the fire-resistors B, to B, and the diodes D to D, when a pulse signal is applied to the first common terminal P, by the pulse generator PG. Therefore to all the input terminals of the detector A, pulse signals are simultaneously transmitted and a pulse signal is caused to appear at the output terminal of the detector A,. In

this case the alarm or warning circuit may be set in such a way not to operate an alarm or a warning light.

II. An abnormal state of the fire-resistors B, to B,,.

If, for example, the fire-resistors B, is disconnected or grounded, namely, is in an abnormal state, and the others are in good condition, a pulse signal does not appear at the connection point I, even if a pulse signal is applied to the first common terminal P,. Therefore, to the input terminals of the detector A, only the pulse signals transmitted through the output terminal of the pulse generator PG and the connection points P P and P,,,' are applied and a pulse signal does not appear at the output terminal of the detector A, since the detector comprises an AND circuit. In this case the alarm or warning circuit may be set to operate, whereby failure of the fire-resistor can be detected.

In the present embodiment it should be noted that, although a certain pulse signal is transmitted to the common terminal P through the diodes D to D,,, this pulse signal is not transmitted to the connection point P since the diode D is connected in a backward direction with respect to such a pulse signal. In other words, the connection point P between the fire-resistor B, and the diode D electrically isolates pointP, against the pulse signals transmitted through the other fireresistors B to B,,.

It will be easily understood that if all or any of the other fire-resistors B to B, has failed, an output pulse does not appear at the output terminal of the detector A, in the same way as mentioned above.

It will be furthermore understood that even in the case wherein the diodes D, to D are respectively connected to the fire resistors B, to B, as shown in FIG. 1, whether any of the diodes has failed can be checked in the same way.

Furthermore, it is necessary to check for failures of the circuits comprising the fire-resistors B, to B and the diodes D to D,,, and attention is again directed to FIG. 1 and FIG. 2 with an explanation as follows.

Such a check can be effectively carried out by using the frequency dividers F, to F and the detector A,.

During time 1, between t, and an output signal of the frequency divider F, is applied to the connection point P and a pulse signal appears at the second common terminal P unless the fire-resistor B, and the diode D are defective. Since no pulse signal is transmitted from the pulse signal generator PG and the frequency divider F to F, during the time period and the diode D, is connected in backward direction with respect to the pulse signal applied to the terminal P no pulse signal is transmitted to the terminal P, through the other circuits. N0 pulse signal is transmitted to the terminal P,,, if the series circuit which comprises fireresistor B, and the diode D is defective, namely disconnected or shorted to ground. The pulse detector A, checks the signal from the frequency divider F, and the signal from the terminal P In the absence of the signal from the terminal P the alarm circuit may be set to operate in order to notify the abnormal state to the driver. Thus, the other circuits each comprising the fire-resistor of B to B and the diode of D to D are checked successively in the same way. As can be seen from the foregoing description, it should be noted that each of the terminals P, to P is electrically isolated by each of the diodes D, to D respectively, from the check signal transmitted through the other circuits.

The fire-resistors B, to 8., might be checked by applying pulse signals to the terminals P to P and by detecting the pulse signals which are to appear at the terminals P to P However, where at least one of the diodes D to D is defective, the circuit does not operate since the diodes D, to D are connected to the fire-resistors B, to B in series.

As can be seen from the foregoing description in this embodiment the circuit line comprising the fire-resistor B, and the diode D, can be checked by applying a check signal to the terminal P, which is common to all the circuit lines and by detecting an output signal at the connecting terminal P between the fire-resistor B, and the diode D Also, the circuit line of the fire-resistor B and the diode D can be checked by applying a check signal to the connecting terminal P between the fire-resistor B and the diode D, and by detecting an output signal at the other common terminal P Each circuit can be checked separately, since it is electrically isolated by the diodes from the check signal which is to be transmitted through the other circuits. Also, since the mean value of current which flows in the fireresistors during checking is very small, it hardly occurs that the fire-resistors are set in operation by the check signal.

Although in the above embodiment, the frequency dividers F, to F, are employed in order to provide shifted pulse signals to each circuit, the invention is not limited thereto. Other circuit means which can provide predetermined check-signals, for example, pulse signal generators which can provide pulse signals having a predetermined waveforms and a predetermined interval can also be applied. Also, although the pulse detectors of this invention comprise AND circuit, other circuits such as NAND circuits etc. which can detect check signals can also be applied.

As described above, the present invention provides a failure check circuit system in a circuit comprising a plurality of circuit elements such as resistors for firing means connected in parallel between a first and a second common terminal wherein a plurality of diodes are connected respectively in series between the circuit elements and the second common terminal, a check signal is applied to the first common terminal, failure of the circuit elements is checked by detecting the output signals appearing at the connection points between the circuit elements and the diodes. The present invention further provides a failure check circuit system in a circuit having a plurality of serial unit circuits each comprising a first diode, a circuit element such as resistor used as a firing means and a second diode connected in parallel between a first and a second common terminal, wherein a check signal, such as a pulse signal, is applied to the first common terminal and the output signals appearing at the connection terminals between the circuit elements and the second diodes are detected, or wherein check signals such as pulse signals, are applied to the connection terminals between the first diodes and the circuit element and the output signals appearing at the second common terminal are detected.

According to the present invention, in a circuit comprising a plurality of circuit elements connected in parallel the existence of a failure in each unit circuit may be effectively checked and the mean value of signal current may be reduced by using a small signal such as a pulse signal, whereby misoperation of the firing means due to the signal current may be prevented. Furthermore, in order to electrically isolate the signal paths in the unit circuits from each other the failure check circuit according to the present invention can be easily and simply constructed by using diodes only.

This invention may be applied not only to a failure check circuit system for an air-bag system for vehicles, but also to fire-alarm system, other firing means to simultaneously fire or blow-up many portions, etc.

While the invention has been described with reference to particular embodiments, this description is not meant to be construed in a limiting sense, but only illustrative of the principles involved. Various modifications of the embodiments described above will be apparent to persons skilled in the art upon reading this specification.

We claim:

1. A failure check circuit comprising:

a plurality of unit circuits each comprising a resistor and a diode connected in series;

connection means for connecting said unit circuits in parallel between a first and a second common terminal;

means for supplying a check signal to said first common terminal; and

detecting means for detecting the existence of signals transmitted from said check signal supplying means to the connection points between said resistors and the diodes.

2. A failure check circuit according to claim 1, wherein said detecting means comprises a logic circuit and has a plurality of input terminals and an output terminal, said input terminals being respectively connected electrically to said connection points between said resistors and said diodes and to said first common terminal.

3. A failure check circuit comprising:

a plurality of serial unit circuits each comprising a first diode, a resistor and a second diode which are connected in series;

connection means for connecting said serial unit circuits in parallel between a first and a second common terminal, so as to directly connect said first and second diodes with said first and second common terminals, respectively;

means for supplying a first check signal to said first common terminal; and

means for detecting the signals transmitted from said check signal supplying means to the connection points between said resistors and said second diodes. 4

4. A failure check circuit according to claim 3, wherein said detecting means comprises a logic circit and has a plurality of input terminals and an output terminal, said input terminals being electrically connected to said connection points between said resistors and said second diodes and to said first common terminal.

5. A failure check circuit according to claim 4, comprising a second means for supplying second check signals to the connection points between said first diodes and said resistors and a second detecting means for detecting the signal transmitted from said second means for supplying second check signals to said second common terminal.

6. A failure check circuit according to claim 5, wherein said second detecting means comprises a logic circuit and has a plurality of input terminals respectively connected to said common terminal and to said connection points between said first diodes and said resostors.

7. A failure check circuit according to claim 6, wherein said second check signals comprise pulse signals shifted in time with respect to each other.

8. A failure check circuit according to claim 3, wherein said first check signal supplying means cmprises means for generating a series of pulses.

9. A failure check circuit according to claim 5, wherein said means for supplying second check signals comprises a plurality of frequency dividers, the inputs of which are connected in common to the output of said first check signal supplying means and the respective outputs of which are connected to respective connection points between said first diodes and resistors.

10 A failure check circuit according to claim 9, wherein each of said frequency dividers has a different frequency division characteristic.

11. A failure check circuit according to claim 3, wherein each of said first and second diodes is connected to pass current in the same direction between said first and second common terminals.

12. A failure check circuit according to claim 1, wherein said check signal is supplied to said first common terminal for checking the condition of said resistOl'S.

13. A failure check circuit according to claim 3, wherein said check signal is supplied to said first common terminal for checking the condition of said resistors.

14. A failure check circuit according to claim 3, wherein said plurality of serial unit circuits serve for activating an occupant safety device of a vehicle, and said resistors of said unit circuits are firing resistors for activating the safety device.

15. A failure check circuit according to claim 5, wherein said plurality of unit circuits serve for activating an occupant protective safety device of a vehicle, and said resistor of said unit circuits are firing resistors for activating the occupant protective safety device. 

1. A failure check circuit comprising: a plurality of unit circuits each comprising a resistor and a diode connected in series; connection means for connecting said unit circuits in parallel between a first and a second common terminal; means for supplying a check signal to said first common terminal; and detecting means for detecting the existence of signals transmitted from said check signal supplying means to the connection points between said resistors and the diodes.
 2. A failure check circuit according to claim 1, wherein said detecting means comprises a logic circuit and has a plurality of input terminals and an output terminal, said input terminals being respectively connected electrically to said connection points between said resistors and said diodes and to said first common terminal.
 3. A failure check circuit comprising: a plurality of serial unit circuits each comprising a first diode, a resistor and a second diode which are connected in series; connection means for connecting said serial unit circuits in parallel between a first and a second common terminal, so as to directly connect said first and second diodes with said first and second common terminals, respectively; means for supplying a first check signal to said first common terminal; and means for detecting the signals transmitted from said check signal supplying means to the connection points between said resistors and said second diodes.
 4. A failure check circuit according to claim 3, wherein said detecting means comprises a logic circit and has a plurality of input terminals and an output terminal, said input terminals being electrically connected to said connection points between said resistors and said second diodes and to said first common terminal.
 5. A failure check circuit according to claim 4, comprising a second means for supplying second check signals to the connection points between said first diodes and said resistors and a second detecting means for detecting the signal transmitted from said second means for supplying second check signals to said second common terminal.
 6. A failure check circuit according to claim 5, wherein said second detecting means comprises a logic circuit and has a plurality of input terminals respectively connected to said common terminal and to said connection points between said first diodes and said resostors.
 7. A failure check circuit according to claim 6, wherein said second check signals comprise pulse signals shifted in time with respect to each other.
 8. A failure check circuit according to claim 3, wherein said first check signal supplying means comprises means for generating a series of pulses.
 9. A failure check circuit according to claim 5, wherein said means for supplying second check signals comprises a plurality of frequency dividers, the inputs of which are connected in common to the output of said first check signal supplying means and the respective outputs of which are connected to respective connection points between said first diodes and resistors.
 10. A failure check circuit according to claim 9, wherein each of said frequency dividers has a different frequency division characteristic.
 11. A failure check circuit according to claim 3, wherein each of said first anD second diodes is connected to pass current in the same direction between said first and second common terminals.
 12. A failure check circuit according to claim 1, wherein said check signal is supplied to said first common terminal for checking the condition of said resistors.
 13. A failure check circuit according to claim 3, wherein said check signal is supplied to said first common terminal for checking the condition of said resistors.
 14. A failure check circuit according to claim 3, wherein said plurality of serial unit circuits serve for activating an occupant safety device of a vehicle, and said resistors of said unit circuits are firing resistors for activating the safety device.
 15. A failure check circuit according to claim 5, wherein said plurality of unit circuits serve for activating an occupant protective safety device of a vehicle, and said resistors of said unit circuits are firing resistors for activating the occupant protective safety device. 